Apparatus for engraving a cylinder with repeated overlapping patterns

ABSTRACT

Method and apparatus for controlling the scanning and engraving heads associated respectively with a rotating cylinder having a master pattern thereon and a rotating cylinder on which a halftone screen printing form pattern of the master is to be produced. The control is such that the heads are intermittently stepped so that the scanning and engraving paths each are in the form of a series of axially spaced incomplete circumferential lines with the end of each such line being joined to the beginning of the next line by a short helical line. Preparation for the subsequent generation of a control signal to stop engraving is effected in response to stepping movement of the heads and the actual stop signal is generated after the stepping movement so that engraving will always actually stop at some point along the next circumferential line while neither head is moving. Thereafter, further stepping of the engraving head is suspended until the engraving is to be restarted so that the engraving head &#39;&#39;&#39;&#39;idles&#39;&#39;&#39;&#39; along the path on which engraving ceased. The signal to restart engraving is timed to occur immediately prior to the point at which the stop engraving signal occurred so that there is always the slight overlap between stop and restart, and no non-engraved gaps occur between stop and restart.

United States Patent 1969, abandoned.

[30] Foreign Application Priority Data Apr. 2, i968 Netherlands 6804633 52] US. Cl. 178/6.6 B [51] lnt. Cl. H04n M04 [58] Field of Search 178/66 B [56] References Cited UNITED STATES PATENTS 1223914 ll/l96l Boyajean l78/6.6 B 2.881246 4/1959 Fairchild 178/66 B Primary E.raminerTerrell Fears Assistant ExaminerRobert S. Tupper Att0meylohn P. Snyder et a1.

. de Vos et a1. I Earn. 8, i974 l l APPARATUS FOR ENGRAVING A [57] ABSTRA'CT CYLINDER WITH REPEATED OVERLAPPING PATTERNS Method and apparatus for controlling the scanning and engraving heads associated respectively with a rol l IYWBHIOISI Ferdinand Allard de tating cylinder having a master pattern thereon and a C S J Hendrik g rotating cylinder on which a half-tone screen printing Breukelen, both of Netherlands form pattern of the master is to be produced. The con- [73] Assigneez NN. werkspoopAmsterdam trol is such that the heads are intermittently stepped Amsterdam Netherlands so that the scanning and engraving paths each are in I the form of a series of axially spaced incomplete cir- [22] Filed: O t- 4, 1971 cumferential lines with the end of each such line being [211 App]. N01: 185,947 joined to the begipning of the next line by a short helical line. Preparation for the subsequent generation of Related U.S. Application Data a control signal to stop engraving is effected in re- [63] Continuation-in-part of Ser. No. 809,643, March 24, SPOHSB t0 pp movement of the heads and the tual stop signal is generated after the stepping movement so that engraving will always actually stop at some point along the next circumferential line while neither head is moving. Thereafter, further stepping of the engraving head is suspended until the engraving is to be restarted so that the engraving head idles along the path on which engraving ceased. The signal to restart engraving is timed to occur immediately prior to the point at which the stop engraving signal occurred so that there is always the slight overlap between stop and restart, and no non-engraved gaps occur between stop and restart.

17 Claims, '7 Drawing Figures direction of rotation m clutch 20 and l .l l l l 18, 17 reap.

cam 26 --bralcee 19, 21

switch 31 Axial feed of scanner and l l l l l l I atop signalstan; 1 derived from I Iaignal i 47" one revolution PATENTEUJAH 8W4 3.7849739 SHEET 1 U? 4 203 'b i7 7 w 16 q 201 202 6 en. 7 t9 Engraving Head I Engraved Cylinder Master Cylinder t Engraved Cylinder 2nd pattern 1st pattern PATENTED 8W 318%739 sum 2 BF 4 PATENTED JAN 81974 SHEET 3 OF 4 PAIENIEUJIIII 81974 39 784,739

SIIEU u If 4 direction of rotation i gap 46" I I clutch 20 and I I 17 reap,

brakes 19, 21

switch '51 Axlal feed of scanner and engraver engraving starts (t) stop signal start I derived from I I I I I I I I I I I I signal I 7 T i I I IF overlap- I 2%;? 0

I I I I I I I p I7" I l I I I I I l I I I II I2 I3 II IS IS I7 In FIG.6

one revolution APFARATUS FOR ENGRAVING A CYLINDER WITH REPEATED OVERLAPPING PATTERNS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 809,643, filed Mar. 24, 1969, now abandoned.

BACKGROUND OF THE INVENTION I In a conventional system for producing half-tone screen printing forms a master cylinder and a printing form cylinder are rotated synchronously while a scanning head and an engraving head respectively associated therewith are fed axially along the lengths of their associated cylinders. In this case, the scanning path and, likewise, the engraving path are helical lines on the respective cylinders. When the scanning head reaches the end of the scanning cycle for the particular pattern on the master cylinder, a stop is provided to terminate movement of the scanning head and to generate a control signal to stop the movement of the engraving head and to terminate the engraving operation. For practical reasons, it is impossible immediately to arrest the motion of the engraving head and, for this reason, the engraving head will coast to some extent beyond the point at which the control signal was generated. Moreover, the point at which it will actually stop cannot be predicted with repeatable accuracy. If engraving is then restarted after moving the scanning head to a new position or to another master pattern area, there will be an unengraved gap between the two engraved patterns on the printing form cylinder. This is particularly noticeable and deleterious with respect to repetitively engraved patterns along the length of the printing form cylinder from a single master pattern on the master cylinder wherein the scanning head, upon reaching the end ofone scan cycle, is returned to the initial scanning position and so forth for as many repetitive patterns as are to be engraved. It is only with extreme difficulty that repetitive patterns with minimal gap can be provided. The only other alternative is to provide the master cylinder with repetitive patterns itself but this is an extremely costly solution and is, for the most part, impractical.

BRIEF DESCRIPTION OF THE INVENTION The present invention overcomes the above-noted difficulties by virtue of the fact that the motions of the scanning and engraving heads are modified so that each is moved axially ofits associated cylinder only intermittently so that the scanning and engraving paths are each in the form of a series ofcircumferentiallines extending substantially completely around the circumference of their associated cylinders with the end of one line being joined to the beginning of the next by a short helical line to provide continuous and complete scan ning and engraving paths. With such an arrangement, it is possible to effect both the control signal to stop engraving and to restart engraving while the scanning head and the engraving head are not moving, thereby eliminating the aforesaid coasting problem. To assure positively that there will be no gap between stopengrave and restart-engrave, preparation for the stop' engrave signal is initiated in response to one of the stepwise movements of the heads and the stop signal is actually generated after the heads have finished their stepwise movements so that the point at which the engraving head actually stops engraving will occur along the length of one of the circumferential lines and, thereafter, stepwise movements of the engraving head is suspended until after engraving has been restarted. The scanning head is moved to the new position and the signal to restart engraving and commence subsequent stepwise movements for effecting another pattern is timed with respect to the rotation of the cylinders to occur slightly before the point at which the stop-engrave signal was generated, thereby to produce a slight overlap of engraving during recommencement or restarting of engraving. In this way, no gaps or unengraved portions will occur between subsequent pattern portions on the printing form cylinder. The fact that the overlapped engraved portions may not be in response to identical pattern portions is barely noticeable and is, in any event, substantially less deleterious than the aforementioned gaps extant in the prior art. Moreover, when repetitively engraving on a printing form cylinder from a single master pattern in which the last line of the pattern is identical with the first line thereof, the overlap in engraving will not be noticeable at all.

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. II is a diagrammatic view illustrating the problems associated with the prior art;

FIG. 2 is a view similar to FIG. I but showing the scanning line path according to the present invention;

FIG. 3 is a view similar to FIGS. I and 2 but showing the engraving line path associated with the present invention and, more particularly, the manner in which repetitive patterns are produced;

FIG. 4 is a diagrammatic view illustrating a preferred embodiment of the invention;

FIG. 5 is a perspective view showing major portions of the preferred embodiment of the invention;

FIG. s is a timing diagram showing several steps of operation; and

FIG. 7 is a diagram showing the circuit by means of which stop and start signals are generated.

DETAILED DESCRIPTION OF Til-IE INVENTION With reference at this time more particularly to FIG. I, a printing form cylinder is indicated therein generally by the reference character P which is rotating about the axis A and relative to which a scanning head is moving axially therealong to engrave according to a master pattern along the helical line H as shown. When the scanning head associated with the master cylinder engages a stop indicating the end of a scanning cycle, a stop signal is generated while the engraving head is at the point a on the helical engraving line H, the cylinder P continuing its rotation. inevitably, there will be a slight time lag after the generation of the stop signal at the point a before the engraving action actually stops, and the point at which engraving actually stops is indicated by the point 19. Further, the inertia of the engraving head will be such that the point at which its physical travel stops will be even further delayed in time as is indicated by the point c and, in particular, this latter point is very unpredictable. As a consequence, the points a, b and c lie in spaced relation as shown so that upon recommencernent or restarting of engraving, even if the engraving head commences engraving immediately upon reception of the restart signal, a gap g in which no engraving appears inevitably is produced.

The principles according to the present invention can be ascertained from a study of FIGS. 2 and 3 showing the master cylinder and the engraved cylinder respectively. ln these two figures, the two cylinders are shown in a condition where there are rotating in unison and as will be hereinafter described in detail, the respective scanning and engraving heads are intermittently stepped axially along the cylinders which takes place during a rotation angle of about 60 for each cylinder. At other times, the scanning and engraving heads are stationary with the net result at the scanning and engraving paths each are in the form of a series of circumferential lines l with the end of each such being joined to the beginning of the next through the medium of a short helical line portion h, see particularly FIG. 2. During the stepwise movements of the heads which occur during completion of the last line of the cycle, such last line being designated by the beginning m and end n thereof, the scanning head engages a stop and prepares the system for subsequent generation of a stop-engrave signal which is generated after the end point n is reached and while the engraving head is motionless. Th us, the actual point at which the engraving stops will occur on the next circumferential line portion beyond the last scanned line defined between the points m and n, FIG. 3 being correspondingly marked for the beginning and the ending of the last engraved line. At this time, further stepwise motion of the engraving head is suspended and, at the same time, mechanism is operated to return the scanning head to its initial position, the engraving of repetitive patterns from a single master being assumed. Due to inertia effects in the system, and other lags, the point at which the scanning head starts to return may be at a point such as is indicated by the point r in FIG. 2, the scanning head describing a helical reversed line back to the point s on the first line ofthe master at which it has been returned to its initial scanning poition. As will also hereinafter be described in detail, a start or restart-engrave signal is generated at the point t which, as shown, is slightly in advance of the position of the point at which the stop engrave signal is generated so that the engraving head will begin engraving again by the time the relative position I of FIG. 3 is reached so that the line 1' becomes the first line of the next engraved pattern, whereafter the sequential and successive stepping actions take place both for the scanning and the engraving head as previously described and with the reengraving or overlap in engraving occurring in the short segmental portion between the points t and 0 of FIG. 3. Particularly if the first and last lines of the master pattern are identical, this overlap in engraving will not be detectable at all. On the other hand, even if there is substantial difference in signals generated during the overlap as between the initial engraving thereon and the subsequent engraving thereon, the effect is not nearly so deleterious as is occasioned by the aforementioned gaps produced by prior art techniques. In FIG. 3, after recommencement or restarting of the engraving for the next pattern, the dash dot lines of engraving are shown in which area the second pattern will be produced, and so on for as many patterns as are desired along the axial length of the engraved printing cylinder. With reference now to FIG. 4, a preferred embodiment of the invention for carrying out the principles described hereinabove is shown. In this figure, the master cylinder is designated by the reference character 1 whereas the printing form cylinder is designated by the reference character 2. The machine includes a main frame indicated generally by the reference character F having ways or guide members W and W for the scanning head 3 and the engraving head 4 respectively, there being provided lead screws 25 and 25' respectively for advancing the scanning head 3 and the engraving head 4 axially with respect to the cylinders and 1 and 2 as will be hereinafter described. The two cylinders l and 2 are engaged at one end each thereof by the driving spindles or chucks 5 and 5' and tail stock devices 6 and 6' are supported in the usual manner on the respective ways W and W and carry the adjustable tail stock centers 5" and 5", as shown whereby the cylinders 1 and 2 are supported about fixed axes and are driven in unison with their respective members 5 and 5.

A main drive motor 14 is provided with an eddy current clutch for synchronization purposes and its shaft 32 carries a drive sprocket 33 by means of which the chain 34 drives the sprocket 33 on the shaft 35. A screen generator device 13 is connected to the shaft 35 whose purpose is to provide an output signal coordinated with the speed or rotation of the cylinders 1 and 2 to produce the requisite number of engraving pulses per revolution of the engraving cylinder 2, such device forming no part of the present invention.

The shaft 35 carries a gear 36 which is in mesh with the gear 37 on the shaft 38, which shaft constitutes the main drive shaft for the assembly and may be provided with a brake 29 by means of which the entire mechanism may be stopped. Transmission assemblies 10 and 10' carry the drive from the main shaft 38 to the two cylinders 1 and 2, the former through the intermediary I of the main gear which drives the shaft 51, and through the gear train 52,53 or through the gear train 54,55 of the auxiliary transmission 11 to the shaft 56 which drives the chuck 5 previously described. A dog clutch 9 is provided on the shaft 56 for engagement either with the gear 53 or with the gear 55, the former for effecting unison rotation of the cylinders 1 and 2 and the latter for effecting a 2:1 drive ratio between the cylinders 1 and 2.

The transmission 10' includes the gear 57 which,- like the gear 50 engages the common gear 58 of the shaft 38, and the gear set 59 and 60 for driving the shaft 61 which is coupled to the chuck 5' for the cylinder 2. A dog clutch 8 is provided selectively to couple the shaft 61 to the gear 60 and the shaft 61 carries a cam 26 engaging with a follower 39 to actuate the mechanism 27 which reciprocates the rods 40 and 41 in the manner more particularly pointed out hereinafter to effect the intermittent stepping motions of the cylinders l and 2 by partial rotations, of the lead screws 25 and 25'.

Reference characters 12 and 16 on the shafts 56 and 61 respectively represent, in the case of the device 12, a magnetic memory device forming no part of the pres ent invention by means of which repetitions of the master form circumferentially on the printing cylinder 2 may be effected. The device 16 is a pulse generator which produces pulses for actuating the engraving member at a selected rate per revolution of the cylinder 2. The details of the circuit 16 may be ascertained from the description of my copending application Ser. No. 185,946, filed Oct. 4, 1971.

As mentioned hereinbefore, the rods 40 and 41 reciprocate in timed relationship with the rotation of the cylinder 2 and these rods are connected to the several clutches l7, l8 and 20, as diagrammatically illustrated in FIG. 4. Members 19 and 21 are brake devices which are normally engaged to prevent rotation of the respective lead screws 25 and 25' but which are deenergized by the mechanism 16 while, at the same time, the clutches l8 and are energized while the rods 4G and 41 are reciprocated in one direction and then the clutches are released when the rods return in the opposite direction, thereby effecting partial rotations of the respective lead screws and 25. In this operation, it is evident that the two lead screws 25 and 25' will be rotated in the same direction and since they are of the same direction of thread, the scanning head 3 and the engraving head 4 will he stepped in the same direction axially of their respective cylinders 1 and 2. To allow for mirror image engraving, the clutch l7 selectively is actuated rather than the clutch 18 which, through the reversing gear set 44,45, imparts the opposite direction of rotation to the lead screw 25 and thereby feeds the scanning head in the direction opposite to the direction imparted to the engraving head 4.

Associated with the scanning head screw 25 is a fast rewind or return motor 23 which is coupled through the sprocket 62, chain 63, sprocket 64 and clutch 22 to the shaft 43 for operating the lead screw 25 to return the scanning head to an initial scanning position when repetitive scannings of the master pattern are to be provided. Similarly, a fast return motor 24 is provided for the lead screw 25 as will be clearly evident.

To complete the general description in association with FIG. 4, two stop switch members and 31 are shown adjustably positioned on the lead screw 25. The stop switch 31 is adjusted to be engaged by the scanning head 3 at the end of the scan cycle as described hereinabove which, through the control circuit I08, releases the brake 19, steps the clutch 22, and maintains the clutches l7, l8 and 20 deenergized while the motor 23 returns the scanning head to its initial scanning position whereupon it engages stop switch 30 which prepares the scanning head for a start engrave operation in association with the engraving head 4 which has remained in its last position during the return movement of the scanning head, as has been described hereinabove. The next repetitive scanning and engraving cycle is then initiated.

With reference to FIG. 5, certain of the components whose construction is not readily apparent from FIG. 4 are shown. Principally, the cam 26 and follower 39 shown wherein it will be seen that the follower is carried by an arm 39' fixed to a shaft 70, the shaft 70 being journalled in a fixed member 71 and carrying the two upstanding fingers 72 and 73 which project through openings in respective arms and 4t, as shown. The two arms have followers 74 and 74 which are adaptively engaged by the fingers 72 and 73 to impart motion to the rods 40 and 41 toward the right in FIG. 5, the return motion being provided for by the respective springs 76 and 77 as shown. The strokes of the rods 4b and 41 are separately adjustable by means of the carrier blocks 78 and 79 which may be raised or lowered by means ofthe adjusting bars 42 and 42. The two carrier blocks 78 and 79 carry cars 80 and 81 which are provided with journal shafts such as the shaft 82 by means of which the respective links 83 and 84 are connected thereto, the upper ends of these links being pivoted to the ends of the respective rods 40 and 41 as shown. Thus, by raising the carrier blocks 78 and 79,

the points at which the followers 74 and engage the fingers 72 and '73 is displaced further from the center or axis of the shaft 7'0 so as to impart a greater throw to each of the rods db and ll and vice versa.

The two rods 4% and ll are pivoted by means of pins 35 and $6 to the extension bars ltl and ll, to the free ends of which the previously mentioned springs 76 and 77 are anchored and two pins 87 and 38 on the extension ll secure same to the respective levers 89 and 9% associated with the respective clutch devices 17 and lb. Similarly, a pin 9i connects the bar ill to the lever 92 associated with the clutch Ztl.

A preferred embodiment of the stop and start portions of the control circuit M8 for effecting the operation as above described is shown in FIG. 7, and a timing diagram illustrative of the control operations is shown in FIG. 6, to which figures reference is now had. The pick-up heads as and 47' (FIG. 5) operate in conjunction with the gaps 4n" and d7 in the discs and 47 such that when the beginnings of the gaps are encountered, negative-going pulses are produced thereby whereas when theends of the gaps are reached, positive-going pulses are produced. These pulses are used with the logic circuit of FIG. 6 to provide the desired control for generating the stop and start signals. It is to be understood that the inverse logic could as well be used and it will further be understood that the logic circuitry for effecting the stepwise motion of the heads, for initiating return of the scanning head, for suspending stepwise motions of the heads during such return motion, and for disabling the engraving member during such return motion is not illustrated in FIG. 7. The omitted funtions are prefectly straightforward logic operations which will be obvious to those in the art.

The direction of rotation of the control discs 46 and 47 is counterclockwise in FIG. 5. The disc 46 controls the stepping motions of the heads. Thus, when a negative-going pulse is generated at the time t, (FIG. 6) by the pick-up 4-6 in consequence of the gap as" being encountered, logic circuitry is activated to deenergize the brakes l9 and 2ll and simultaneously to energize or engage the clutches I8 and 24} or the clutches l7 and 2t), dependent upon whether the scanning head is to be stepped in the same or the opposite direction to the engraving head. When the clutches are engaged and the cam an is operative to actuate the levers W and 41 at time 2 the stepping motions will take place, as indicated in FIG. 6. These stepping motions are terminated at time 1 due to deenergization of the clutches and energization of the brakes, as shown. When the last line of the pattern is scanned, and during the stepping motions occuring within the time period t t the switch Ell is contacted and it produces a step signal which causes the normally low output of the flip-flop 209 to go high, which output remains high until the switch 31 is deactivated upon return motion of the scanning head (FIG. 6 At time 2 a negative-going pulse is produced by the head 47 but same does not offset the normally low output of the flip-flop Elli. Then, the end of the gap 47" is reached and the head 47' produces a positivegoing pulse at time t, which causes the output of the flip-flop Ztlll to go high. At this time, the AND gate 22 produces an output causing the normally low output from the flip-flop to go high so that when the next pulse from the pulse generator to for the engraving device occurs, a stop signal will be produced at the output of the AND gate 2ll4. This stop signal causes override of the stepping actions of the engraving head by keeping the brake 21 engaged and the clutch disengaged until after the switch 30 is engaged by the scanning head, and also causes the brake 19 to be deenergized and both clutches 17 and 18 to remain deenergized until after the switch 30 is engaged. Further, the stop signal causes the clutch 22 to become energized to cause the scanning head to be returned until such return is terminated by the switch 30.

When the switch 30 is engaged by the scanning head, the output of the flip-flop 206 is caused to go high and then when the gap 47" is first encountered by the head 47, the negative-going pulse (time pointt is inverted at 208 causing the second input to the AND gate 205 to go high. The third input to the AND gate 205 properly times the start signal output from the AND gate 205 so that the engraving device may start the first engraving action in proper synchronism with the pulse signals from the circuit 16.

It is to be understood that the aforesaid copending application, Ser. No. 185,946, filed Oct. 4, l9? 1 a continuation-in-part of Ser. No. 823,389, filed May 9, l969, is incorporated herein by reference.

We claim: 1. In a machine for electromechanically producing gravure forms which are repetitive reproductions of a single master, a first cylinder having said single master thereon, a second cylinder upon which said repetitive reproductions are to be formed, scanning means associated with said first cylinder for producing outputs indicative of the instantaneous local intensity of the master as the first cylinder revolves with respect to the scanning means, engraving means associated with said second cylinder for effecting periodic penetrations of the surface of said second cylinder in which the depth of each penetration is in accord with the instantaneous output of said scanning means, first feed means for translating said scanning means axially with respect to said first cylinder, second feed means for translating said engraving means axially with respect to said second cylinder, and means for continuously rotating said first and said second cylinders at a selected speed ratio, the improvement comprising:

control means for actuating said first and said second feed means during a minor portion only of each revolution of said scanning means whereby consecutive scanning and engraving line paths swept past the scanning means and the engraving means respectively each are in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of the associated cylinder and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion;

return means responsive to a terminal movement of said scanning means effected by said control means for returning said scanning means to the first scan line of the master and for disabling said control means during such return whereby said engraving head remains in axially fixed relation to said second cylinder; and

repeat means responsive to return of said scanning head to said first scan line for initiating a subsequent scan-engrave cycle in advance of the point on which engraving ceased and while said engraving means is in said axially fixed relation to cause element generating sequential signals during successive revolutions of said second cylinder, the second of which successive signals causes cessation of engraving and the first of which causes engraving to restart whereby restarting of engraving during one revolution of the second cylinder overlaps engraving produced during a prior revolution.

4. in a machine as defined in claim 3 wherein said common element is a disc rotating in unison with said second cylinder and having circumferentially spaced signal producing means thereon.

5. in a machine as defined in claim 3 wherein said control means includes reciprocating-to-rotary motion means for periodically actuating said first and second feed means correspondingly to step said scanning means and said engraving means axially of their cylinders.

6. In a machine as defined in claim 5 wherein said common element is a disc rotating in unison with said second cylinder and having circumferentially spaced signal producing means thereon.

7. In a machine for electromechanically producing gravure forms, in combination:

cylinder means upon which engraving of consecutive patterns is to be performed;

engraving means for engraving upon said cylinder means;

means for rotating said cylinder means continuously during the engraving sequence;

means for stepping said engraving means axially along said cylinder means only once during each of a successive number of revolutions of said cylinder means to describe consecutive paths of said .engraving means relative to said cylinder in which each path is in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of said cylinder and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion;

means for actuating said engraving means during said successive revolutions to engrave at least two consecutive patterns on said cylinder means;

means for disabling said means for stepping and said means for actuating at the end of the first pattern whereby engraving stops while the engraving means is located at a selected position axially along said cylinder means; and

means for enabling said means for stepping and said means for actuating so as to start a second pattern overlapping the first pattern while said engraving means is at said selected position and in advance of the point at which engraving ceased on the first pattern.

8. In a machine as defined in claim 7 wherein said means for actuating causes said engraving means to 9 produce contiguous, repetitive patterns along said cylinder means.

9. In a machine as defined in claim 8 including a master pattern controlling said means for actuating.

10. In a machine as defined in claim 9 wherein the first and last lines of said master pattern are identical. iii. In amachine as defined in claim 9 wherein said master pattern is engraved in mirror image fashion on said cylinder means.

12. in a machine as defined in claim llil wherein the first and last lines of said master pattern are identical.

13. A machine for producing gravure forms comprising, in combination:

pattern cylinder means and gravure cylinder means coupled for common rotation at a selected speed ratio; means for imparting incremental motions of said scanning means and said engraving means axially along their respective cylinder means only once during each revolution of such cylinder means whereby scanning and engraving paths are described each in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of the respective cylinder means and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion; means for continuously rotating said pattern cylinder means and said gravure cylinder means during an engraving sequence;

scanning means and engraving means associated respectively with said pattern cylinder means and said gravure cylinder means for respectively scanning said pattern cylinder means and for engraving said gravure cylinder means;

means for periodically uncoupling said scanning means and said engraving means and repetitively returning said scanning means to an initial position whereby said scanning means repetitively traverses a selected length of said pattern cylinder means while said engraving means traverses contiguous successive lengths of said gravure cylinder means; and

means for causing partial overlap of engraving at the contiguities of said successive lengths whereby the engraving on said gravure cylinder means is uninterrupted between such successive lengths.

M. A machine according to claim 13 wherein said pattern cylinder means is provided with a selected pattern and said engraving means produces repetitive gravure images thereof.

Zl5. A machine according to claim l4 wherein the first and last lines of said selected pattern are identical.

16. A machine as defined in claim I l wherein said gravure images are mirror images of said selected pattern.

17. A machine according to claim in wherein the first and last lines of said selected pattern are identical. 

1. In a machine for electromechanically producing gravure forms which are repetitive reproductions of a single master, a first cylinder having said single master thereon, a second cylinder upon which said repetitive reproductions are to be formed, scanning means associated with said first cylinder for producing outputs indicative of the instantaneous local intensity of the master as the first cylinder revolves with respect to the scanning means, engraving means associated with said second cylinder for effecting periodic penetrations of the surface of said second cylinder in which the depth of each penetration is in accord with the instantaneous output of said scanning means, first feed means for translating said scanning means axially with respect to said first cylinder, second feed means for translating said engraving means axially with respect to said second cylinder, and means for continuously rotating said first and said second cylinders at a selected speed ratio, the improvement comprising: control means for actuating said first and said second feed means during a minor portion only of each revolution of said scanning means whereby consecutive scanning and engraving line paths swept past the scanning means and the engraving means respectively each are in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of the associated cylinder and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion; return means responsive to a terminal movement of said scanning means effected by said control means for returning said scanning means to the first scan line of the master and for disabling said control means during such return whereby said engraving head remains in axially fixed relation to said second cylinder; and repeat means responsive to return of said scanning head to said first scan line for initiating a subsequent scan-engrave cycle in advance of the point on which engraving ceased and while said engraving means is in said axially fixed relation to cause partial overlap of engraving between successive patterns.
 2. In a machine as defined in claim 1 wherein said control means includes reciprocating-to-rotary motion means for periodically actuating said first and second feed means correspondingly to step said scanning means and said engraving means axially of their cylinders.
 3. In a machine as defined in claim 1 wherein said return means and said repeat means include a common element generating sequential signals during successive revolutions of said second cylinder, the second of which successive signals causes cessation of engraving and the first of which causes engraving to restart whereby restarting of engraving during one revolution of the second cylinder overlaps engraving produced during a prior revolution.
 4. In a machine as defined in claim 3 wherein said common element is a disc rotating in unison with said second cylinder and having circumferentially spaced signal producing means thereon.
 5. In a machine as defined in claim 3 wherein said control means includes reciprocating-to-rotary motion means for periodically actuating said first and second feed means correspondingly to step said scanning means and said engraving means axially of their cylinders.
 6. In a machine as defined in claim 5 wherein said common element is a disc rotating in unison with said second cylinder and Having circumferentially spaced signal producing means thereon.
 7. In a machine for electromechanically producing gravure forms, in combination: cylinder means upon which engraving of consecutive patterns is to be performed; engraving means for engraving upon said cylinder means; means for rotating said cylinder means continuously during the engraving sequence; means for stepping said engraving means axially along said cylinder means only once during each of a successive number of revolutions of said cylinder means to describe consecutive paths of said engraving means relative to said cylinder in which each path is in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of said cylinder and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion; means for actuating said engraving means during said successive revolutions to engrave at least two consecutive patterns on said cylinder means; means for disabling said means for stepping and said means for actuating at the end of the first pattern whereby engraving stops while the engraving means is located at a selected position axially along said cylinder means; and means for enabling said means for stepping and said means for actuating so as to start a second pattern overlapping the first pattern while said engraving means is at said selected position and in advance of the point at which engraving ceased on the first pattern.
 8. In a machine as defined in claim 7 wherein said means for actuating causes said engraving means to produce contiguous, repetitive patterns along said cylinder means.
 9. In a machine as defined in claim 8 including a master pattern controlling said means for actuating.
 10. In a machine as defined in claim 9 wherein the first and last lines of said master pattern are identical.
 11. In a machine as defined in claim 9 wherein said master pattern is engraved in mirror image fashion on said cylinder means.
 12. In a machine as defined in claim 11 wherein the first and last lines of said master pattern are identical.
 13. A machine for producing gravure forms comprising, in combination: pattern cylinder means and gravure cylinder means coupled for common rotation at a selected speed ratio; means for imparting incremental motions of said scanning means and said engraving means axially along their respective cylinder means only once during each revolution of such cylinder means whereby scanning and engraving paths are described each in the form of a circumferentially extending major portion disposed in a plane normal to the rotation axis of the respective cylinder means and a helically extending minor portion connecting the end of each major portion with the beginning of the next consecutive major portion; means for continuously rotating said pattern cylinder means and said gravure cylinder means during an engraving sequence; scanning means and engraving means associated respectively with said pattern cylinder means and said gravure cylinder means for respectively scanning said pattern cylinder means and for engraving said gravure cylinder means; means for periodically uncoupling said scanning means and said engraving means and repetitively returning said scanning means to an initial position whereby said scanning means repetitively traverses a selected length of said pattern cylinder means while said engraving means traverses contiguous successive lengths of said gravure cylinder means; and means for causing partial overlap of engraving at the contiguities of said successive lengths whereby the engraving on said gravure cylinder means is uninterrupted between such successive lengths.
 14. A machine according to claim 13 wherein said pattern cylinder means is provided with a selected pattern and said engraving means produces repetitive gravure images thereof.
 15. A machine according to claim 14 wheRein the first and last lines of said selected pattern are identical.
 16. A machine as defined in claim 14 wherein said gravure images are mirror images of said selected pattern.
 17. A machine according to claim 16 wherein the first and last lines of said selected pattern are identical. 